<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<h1>0</h1>
<script>
  let count=0;
  setInterval(f,1000);
  function  f(){
    count++
    let  h=document.querySelector("h1");
    h.innerText=count;
  }
  //匿名方法定时器
  let timer= setInterval(function (){
    console.log(count)
    if (count==5){
      clearInterval(timer)
    }
  },1000);
  //开启只执行一次的定时器
  setTimeout(function (){
    console.log("时间到!");
  },3000);


</script>
</body>
</html>